"Huge swathes of Gaza have been levelled. We cannot rebuild it with our hands tied behind our backs," said Chris Gunness, spokesman for the UN agency for Palestinian refugees (UNRWA).

"The blockade must end. We are beyond the realm of humanitarian action alone. All those directly and indirectly responsible for the carnage and destruction must engage," he said.

The lifting of Israel's land and sea blockade, imposed in 2006 after Hamas captured an Israeli soldier, has been a key demand of Hamas and the Palestinian Authority at stalled truce talks in Cairo.

At least 65,000 people have seen their homes destroyed in a month of fighting between Israel and Hamas and a "man-made homelessness crisis on an epic scale is unfolding", Gunness warned.

UN agencies and the Palestinian Authority are now working on a reconstruction plan which includes rebuilding water, sewerage facilities and electricity supplies.

"This is an urgent priority. Without it people simply cannot go home. Rubble removal is also an important aspect of this for which we are planning to use local workers to boost the local economy," Gunness said.

Israel went to war against Hamas in Gaza last month with the aim of destroying its arsenal of rockets, which target Israeli towns and cities, and its network of attack tunnels burrowing into Israeli territory.

Gunness said that Israel has legitimate security concerns, but that collective punishment of the 1.8 million Palestinians packed into Gaza had been "ineffective".

"It is time for Israel to enable, not disable. It is time for the world to recognize the blindingly obvious - that the Gaza conflict requires a political solution," he said.

Israel eased restrictions on imports of food and construction materials in 2010 following an international outcry over a botched Israeli raid on a Gaza-bound flotilla which was trying break the blockade, killing 10 Turks.

Some further restrictions were eased after the last Israel-Hamas conflict in Gaza in 2012.

Hamas wants fishing zones extended, and to have a port and an airport.